Ovarian carcinoma (OCa) continues to be the leading cause of death due to gynecologic malignancies. Epidemiological data suggest that progesterone (P4) offers protection against OCa while estrogens promote OCa development. We recently demonstrated in normal and malignant human ovarian surface epithelium (HOSE) cells a growth inhibitory action of P4 and a growth promotional effect of estrogens. P4 was shown to activate an extrinsic apoptosis-initiation pathway that involves caspase-8, but not the intrinsic, mitochondrion-related caspase-9' pathway. Importantly, our results have revealed involvement of the Fas/FasL signaling as an important mechanism of P4-induced apoptosis in normal and malignant OSE cells. This finding has incited us to examine the relationship between this steroid and the TNF-related apoptosis-inducing ligand (TRAIL)TRAIL receptor signaling pathway, which holds greater promises for targetted therapies for a variety of cancers.; TRAIL has several advantages over the other TNF-family ligands;1) it is a "pure" apoptosis-inducer, 2) it has preferential cell kill activity against cancer cells, 3) it has a very favorable in vivo toxicity profile, 4) its apoptotic action is independent of p53 status, and 5) its action is often enhanced by combination with other therapeutic agents. In addition, we have discovered that, contrary to the existing dogma, estrogens down regulate progesterone receptors (PRs) in normal and malignant HOSE cells and therefore can negate the protective effects of P4. We therefore hypothesize that P4 and TRAIL independently and/or synergistically induce apoptosis in HOSE and OCa cells through activation of an extrinsic pathway of apoptosis and offer protection against ovarian cancer while E2 via downregulation of PR can negate the effects of P4. Five broad specific aims have been proposed to test these hypotheses: 1. To characterize and compare the apoptotic responses induced by TRAIL and P4, individually or conjointly, in HOSE and OVCA cell lines in order to discern any synergistic effects. In parallel, the effects of P4 on TRAIL and TRAIL receptor, expression will be studied to gain a better understanding of the mechanistic link between the two. Special attention will be placed on detecting whether the apoptotic response belong to type I (extrinsic alone) or type II (extrinsic plus intrinsic amplification). 2: To compare the efficacies of natural progesterone and synthetic progestins such as MPA and NETA in inducing apoptosis in HOSE and OVCA cell lines and to determine whether they have comparable synergistic actions on TRAIL-induced apoptosis. Their action on activating iNOS via the MAPkinase signaling pathway will also be investigated. 3. To determine the anti-tumor activity of P4, MPA, NETA, and recombinant human TRAIL in vivo. 4. To determine whether estrogens antagonize the P4-induced apoptosis via induction of PR downregulation and to determine which estrogen is most effective. 5. To determine if estrogens and SERMs negate the effects of P4 by blocking the influences of P4 on the expression of TRAIL and TRAIL receptors. Results from this proposal have the potential to generate new strategies for the prevention and treatment of OCa.